LExEn: Hyperthermophiles of the Hydrothermal Vent Subsurface and Their Environmental Tolerance

LExEn：热液喷口亚表层的超嗜热菌及其环境耐受性从深海热液喷口分离的超嗜热古菌在极端高温、高压和极可能的化学毒性下生存和生长。在热液喷口流出物和海底火山爆发产生的固体中分离和检测到这些物质，强烈表明它们也存在于炎热和缺氧的地下环境中。它们在极端的地下热液喷口条件（pH值、硫化物、金属、温度和压力）下生存或生长的能力将表明这些生物是否有潜力成为分布广泛和环境耐受性强的深地下居民。除了温度和一定程度的压力之外，决定喷口超嗜热菌在地下条件下生长和存活的许多关键因素尚未得到测试，因此无法对这些生物的出现范围和环境耐受性进行现实的评估，本项目将测试热液喷口古菌实际上生长在高温、厌氧和有毒热液喷口地下的假设，最有可能是沿着通过多孔或洞穴状岩石的排放流体的流动路径。这些实验将使用四种热液喷口超嗜热古菌，即产甲烷菌詹氏甲烷球菌、异养硫还原菌烟曲霉热球菌、火球菌属菌株GB-D和硫酸盐还原菌深古生球菌。这些古菌被选为厌氧、嗜热代谢的代表，是热液喷口古菌种群的代表，具有承受地下条件的生理潜力。最重要的是，这些属直接从正在进行的海底喷发和喷口巨型羽流中分离出来。我们将在近似的原位条件下系统地测试这些喷口古菌的生长和生存：洋中脊热液喷口及其地下延伸的高静水压力;酸性pH值;以及高硫化物和金属浓度。这些因素将单独测试，并以近似自然情况的方式一起测试。将通过比较单因素和多因素实验来检验以下假设，即这些压力因素对地下环境中热液喷口古菌的生长和存活的协同效应与每个因素单独的效应有很大不同。影响生长和存活的一个重要特征是生物膜的形成，最近才研究了古细菌模型系统。由于生物膜的形成增强了许多细菌的环境耐受性，热液喷口和地下环境中的古细菌生物膜可能对环境压力因素表现出更强的耐受性。换句话说，热液喷口和地球地下生物圈中最具抵抗力的生物可能不是古生菌，而是古生菌生物膜。这些实验旨在整合几个物理和化学因素，这些因素共同决定了地球上一些最极端生命形式的耐受极限。

LExEn: Hyperthermophiles of the Hydrothermal Vent Subsurface and Their Environmental ToleranceHyperthermophilic archaea, isolated from deep-sea hydrothermal vents, survive and grow under extreme heat, pressure, and most likely chemical toxicity. Their isolation and detection in hydrothermal vent effluents and in solids from undersea volcanic eruptions strongly suggest that they also occur in hot and anoxic subsurface environments. Their ability to survive or grow under extreme subsurface hydrothermal vent conditions (pH, sulfide, metals, temperature, and pressure) will show whether these organisms have potential as widespread and environmentally tolerant deep-subsurface inhabitants. With the exception of temperature, and to some degree pressure, many critical factors which determine growth and survival of vent hyperthermophiles under subsurface conditions have not been tested, preventing a realistic assessment of the occurrence range and environmental tolerance of these organisms.This project will test the hypothesis that hydrothermal vent archaea actually grow inthe hot, anaerobic and toxic hydrothermal vent subsurface, most likely along the flow paths of vent fluids through the porous or cavernous rock. Four hydrothermal vent hyperthermophilic archaea will be used for these experiments, the methanogen Methanococcus jannaschii, the heterotrophic sulfur reducers Thermococcus fumicolans, Pyrococcus sp. strain GB-D, and the sulfate reducer Archaeoglobus profundus. These archaea were selected as a cross-section of anaerobic, thermophilic metabolisms which are representative for hydrothermal vent archaeal populations, and have the physiological potential to withstand subsurface conditions. Most importantly, these genera have been isolated directly from ongoing undersea eruptions and vent megaplumes. We will systematically test the growth and the survival of these vent archaea under approximated in situ conditions: high hydrostatic pressure of mid-ocean ridge hydrothermal vents and their subsurface extensions; acidic pH; and high sulfide and metal concentrations. These factors will be tested individually, and together in ways that approximate the natural situation. The hypothesis that the synergistic effects of these stress factors on growth and survival of hydrothermal vent archaea in the subsurface environment will differ considerably from the effect of each factor alone will be tested by comparing single-factor and multi-factor experiments. An important feature which influences growth and survival is biofilm formation, only recently studied for archaea model systems. Since biofilm formation enhances the environmental tolerance of many bacteria, archaeal biofilms in hydrothermal vent and subsurface environments are likely to show increased tolerance to environmental stress factors. In other words, the most resistant organism of hydrothermal vents and the earth's subsurface biosphere may not be an archaeon, but an archaeal biofilm. These experiments aim at integrating several physical and chemical factors which together determine the tolerance limits of some of the most extreme life forms on earth.